1. Field of the Invention
This invention is directed to an improved fuel injection system including an electronically triggered control valve.
2. Description of the Prior Art
One fuel injection system of the type with which this invention is concerned is known from German Patent Disclosure DE 197 01 879 A1 and uses an electrically triggered 3/2-way control valve for controlling the injection times and quantities; this control valve has a control piston, guided in an axial through bore, that connects a high-pressure line leading to an injection valve to a supply line, which delivers fuel from a high-pressure reservoir (common rail), or to a relief line in alternation. To that end, the through bore is subdivided by two valve seats into three annular chambers, into which the supply line, the high-pressure line and the relief line each discharge. Upon a stroke motion, the control piston closes one valve seat as it uncovers the other valve seat. To that end, the control piston has two valve sealing faces, cooperating with the valve seats; the spacing between valve sealing faces is greater than the spacing between the two valve seats. The supply line, that is, the high-pressure side, therefore briefly communicates directly with the relief line, that is, with leak fuel, during a stroke motion of the control piston, so that some of the fuel is diverted via the relief line. The diverted quantity is dependent on the pressure prevailing in the high-pressure reservoir and is sometimes considerably higher than the injection quantity.
The fuel injection system according to the invention for internal combustion engines has the advantage over the prior art that by means of a further valve sealing face, a direct communication between the high-pressure side and the leak fuel is reliably prevented. This leads to markedly reduced diversion quantities and increases the hydraulic efficiency.
In a pressure-controlled injection valve, the control valve can be used to connect an injection cross section of the injection valve, which can be opened by a valve needle of the injection valve, to either the supply line or the relief line. The requisite pumping quantity of the high-pressure fuel pump that supplies the high-pressure side, such as a high-pressure reservoir, is thus less, and furthermore the temperature load on the fuel tank system is reduced because of reduced return quantities at a high diversion temperature.
In a pressure- and cross-section-controlled injection valve, the control valve can also be used to control the injection cross section. Advantageously, the same valves can be used to control both the injection quantity and the injection cross section.